Because of their desirable profile of physical and mechanical properties polycarbonate resins are frequently selected for use in molding articles geared for the medical field. In these application, the resistance of the material to deterioration induced by exposure to sterilizing radiation is often times of prime importance. Articles molded from polycarbonate while meeting most other criteria, fall short in terms of their resistance to gamma radiation. These articles suffer yellowing due to the decomposition of the resin. U.S. Pat. Nos. 4,996,244; 4,996,245; 4,996,246; and 4,996,247 are considered to disclose relevant technology.
The art is noted to include European Patent Application 376,289 which disclosed a relevant polycarbonate composition containing a blend of a polycarbonate derived from a halogenated bisphenol and a polyalkylene glycol or its ether, silyl ether or ester. Also relevant is European Patent Application 359,366 which disclosed relevant gamma radiation resistant polycarbonate compositions which contain an organic halogen compound. Of particular importance in the present context are U.S. Pat. Nos. 4,874,802; 4,904,710 and 4,804,692 which disclosed relevant polycarbonate compositions containing polyether compounds including the stabilizing polyalkylene oxide of the present invention.
While the technical solutions offered to date do in fact reduce the permanent yellowing of polycarbonate compositions and impart desirable stability to the articles molded therefrom, a temporary color change characterizes these compositions. This color may take as long as several weeks to subside, especially in the absence of light. This causes undesirable color changes in tinted or dyed polycarbonate resin. In addition, the long period needed to stabilize the color constrains the producers of sterilized parts because of the long delay before a stable, desirable color is attained.